Failure mechanisms encountered in micro-milling of aligned carbon fiber reinforced polymers

A failure model is proposed to capture the fiber failure mechanisms that occur while machining carbon fiber-reinforced polymer composites at the micro-scale. The model proposes that the failure mechanisms vary as a function of fiber orientation relative to the direction of the tool cutting edge motion. Carbon fibers oriented at 90 and 45 degrees to the direction of motion of the tool cutting edge are proposed to fail predominantly in crushing/compression while buckling- and bending-dominated tensile failures are proposed for the 0 and 135 degree orientations, respectively. Micro-milling slotting tests are conducted to validate the proposed model. Chip morphology, delamination, and cutting forces are the machining responses used for validation. At the micro-scale for the 90 and 45 degree fiber orientations, the short fiber fragments in the chips, low delamination, and high cutting forces all point to a crushing-dominated (compressive) failure. For the 0 and 135 degree orientations, chips containing long fiber bundles, low and high delamination, respectively, and low cutting forces all imply buckling- and bending-dominated (tensile) failures, respectively.